Process of reducing metallic ores with gases



May 15, 1956 T. H. OSTER 2,745,73?

PROCESS OF REDUCING METALLIC ORES WITH GASES Filed NOV. 21, 1952 FLUXCRUSHED ORE WASH METAL wA/R CYCLONE BURNER 3 T0 HEAT RECOVERY FUSED OREWASH All;

METAL r HOT COMBUST/BLE GAS C V C L ONE A/R ZFUEL A/R MOLTEN ME TAL' 8GANGUE T H. O5 75/? INVENTOR EFF/ 77m BY ATTORN EYS United PROCEEES FREDUQENG METALLIQ GEES; WiTT-i GAE Application November 21, 1952, SerialNo. 321,769

12 Claims. (Cl. 75-91) This invention is concerned with the art ofutilizing fuels and more particularly with a process for the combustionof fuels and the concomitant treatment of metallic ores to recover themetallic values therefrom in a more concentrated condition. Thisinvention is related to my copending application, Serial No. 253,890filed October 31, 1951, entitled Combustion Process, to my application,Serial No. 317,282 filed October 28, 1952, entitled Combustion Processand to my application, Serial No. 316,708

led October 24, 1952, entitled Dual Combustion Proces This invention ismore particularly concerned with the utilization of the combustionprocess described for the recovery of metal values from ores in whichthe metal value forms only a small portion of the ore as mined or inwhich the ore is present in a chemical or physical condition which makesits recovery difficult by conventional methods such as pulverizationfollowed by flotation or other differential separation means.

It is contemplated that the process of this invention be carried out ina device known as a cyclone burner. Briefly, this device comprises awater cooled steel cylinder usually placed with its axis slightlyinclined from the horizontal and provided at one end with means for thereception of a stream of fuel and primary air and at the other end withan exit for the products of combustion and an exit for molten slag. Thistype of burner and its operating characteristics are amply and ablydescribed in an article entitled The Horizontal Cyclone Burner by A. E.Grunert, L. Skog and L. S. Wilcoxson appearing at page 613 et seq. ofthe American Society of Mechanical Engineers, Transaction, volume 69,1947. The term cyclone burner employed in the appended claims is limitedto the type of water cooled burner described by Grunert et a1.

As the known supplies of high grade metallic ores have become depleted,it has been necessary to resort to leaner and leaner ores for the metalsnecessary for our day to day life. In these lean ores the desiredmetallic values are associated with large amounts of worthless gangue.To separate the metallic values from the gangue and obtain the desiredhigh metal concentration, it is usually necessary to resort to crushingand grinding followed by a separation step such as flotation,electrostatic separation, magnetic separation, or other proceduredependent upon chemical or physical differences between the metaldesired and the gangue. These concentration procedures are costly andalmost invariably involve a sacrifice of metal values. The higherconcentration of metal desired the higher is usually the loss of metalvalues to the tailing pile. The instant invention has been developed toincrease the range of ores which may be treated without resort to theusual concentration processes.

As described and claimed in the applications mentioned above, it ispossible to operate a cyclone burner with either a solid fuel or fluidfuel, and to introduce a metal ore into the burner and by a judiciouschoice of the oxidation level in the burner, to recover from the burnereither a fused ore or a reduced metal.

In many instances, even when operating with a rela- Yttes Patent 0tively concentrated ore it is difficult to simultaneously maintain thedesired oxidation level within the burner and to maintain a temperaturewhich will keep all materials within the burner except carbon eitherliquid or gaseous. The great majority of metal ores are predominantlysiliceous or combinations of silica with varying amounts of lime andalumina. The upper limit of the temperature necessary to fuse most oresis fixed by the melting point of quartz or about 2600 F. The theoreticalmelting points of pure silica or the various calcium and aluminumsilicates are not attained because of the fiuxing action of variousimpurities and particularly the oxides of iron which are almostinevitably present. To maintain these necessary conditionssimultaneously resort must be had either to highly preheating theincoming air, or to enriching the incoming air with oxygen, or to acombination of these expedients. In many instances when the ganguecontent of the ore is too high, it is impracticable to maintain thenecessary temperature and reducing conditions within the burner due tothe large amount of energy required to heat and melt the gangue. Thisenergy amounts to approximately one thousand British thermal units perpound. To circumvent this difiiculty resort is had to a dual cycloneburner. This method and the associated apparatus are probably bestunderstood by reference to the figure of drawing which is a schematicrepresentation.

In the drawing cyclone burner 1 is shown above cyclone burner 2 and inpractice this arrangement should be followed so that molten materialsmay be transferred by gravity from cyclone burner 1 to cyclone burner 2.it is preferred that practically all of the fuel introduced into thesystem enter cyclone burner 2 and be introduced along with a stream ofprimary air or other oxidizing gas such as oxygen enriched air or oxygenof any desired degree of purity. As those skilled in the art willappreciate, the bulk of the air necessary for combustion in cycloneburners is introduced not in the primary air stream but in a rapidlymoving stream of secondary air which is injected into the burnertangentially so that a swirling motion is set up therein and any givenparticle will pass through the burner in a generally helical path. Theoxidation level in cyclone burner 2 is adjusted to yield the desireddegree of reduction of any metal ore passing through this burner. Whenthe usual fuels such as coal, coke, petroleum or natural or artificialgas is used, the gaseous efliuent from cyclone burner 2 will be very hotand contain large quantities of combustible gases such as carbonmonoxide and hydrogen. This gaseous eflluent of cyclone burner 2 whichis rich in both sensible and latent heat is transferred to cycloneburner 1 through a well insulated conduit and preferably serves as thesole fuel for cyclone burner 1. The gaseous efiluent from cyclone burner1 is of necessity very hot and is passed to a steam generator, or airpreheater or other device for the recovery of its sensible heat. Cycloneburner 1 may discharge into an ordinary boiler and so produce steam forheat or power purposes. It will often be found to be advantageous topass the hot gaseous products of combustion of cyclone burner 1 over amass of crushed ore which is destined for later fusion in cycloneburner 1. This expedient serves the dual function of providing cycloneburner 1 with a preheated supply of ore and of providing an economicalmethod of obtaining preheated air for the cyclone burners. This isaccomplished by providing two masses or" crushed ore and alternatelypassing over each mass combustion air and products of combustion.Inasmuch as the products of combustion emanating from cyclone burner 1are above the melting point of the ore it will usually be necessary toreduce the temperature of these gases slightly either by the use of asmall boiler, or by admixing therewith a small amount of relatively coldgas such as air or stack gas.

Crushed, but not necessarily pulverized ore is introduced into cycloneburner l with, or at least near the point of entrance of the hot fuelgas from cyclone burner 2.

The sensible heat in these hot combustible gases from cyclone burner 2,plus the heat released when they react with the air introduced incyclone burner 11 maintains the interior of cyclone burner 1 above themelting point of the ore, modified if necessary by the addition of anappropriate flux. The molten ore Will form a liquid coating over theinterior of the burner and this liquid will describe a helical pathtowards the discharge end of the burner. The crushed pieces of ore willbe hurled to the inner surface of the burner by centrifugal force andtrapped in the molten ore layer until they are in turn melted.

The fused ore produced in cyclone burner i is transferred immediately tocyclone burner 2 preferably by gravity and through a well insulatedconduit to prevent the loss of heat. The air and fuel introduced intocyclone burner 2 are so proportioned that the interior of this cycloneburner will be maintained under conditions reducing to the metal it isdesired to recover. of the combustion of fuel in cyclone burner 2 servesto maintain this burner at a temperature necessary to maintain all ofthe reactants except carbon in either the liquid or gaseous state and toreduce the ore to the metal. The exact temperature to be maintained, andthe intensity of the reducing conditions to be established in cycloneburner 2 depend upon such factors as the cost of fuel, the cost of ore,the value of the metal produced, and other strictly local factors sothat it is impossible to set these conditions forth quantitatively. Theyshould be determined for each particular operation.

In many instances the operation of this process with air at atmospherictemperatures will be found to be impossible. Under these conditionsresort must be had to the use of highly preheated air or oxygen enrichedair or both. it is to be understood that preheated air or oxygenenriched air are not strictly alternatives, but can be used eitherseparately or together depending upon the ore and local economicconditions. in any event, the heat intro duced into cyclone burner 2 inthe fused ore, plus the heat introduced in the air plus the heat ofcombustion taking place in the burner must equal or exceed the heatleaving the burner in the molten metal and gangue, plus the latent andsensible heat in the hot gas efiiuent plus the heat losses from theburner through radiation, cooling water, etc., plus the heat necessaryfor the reduction of the metal.

Similarly in cyclone burner 1, the sensible heat in the hot gases fromcyclone burner 2, plus the heat of combustion or" these gases, plus theheat brought in in preheated air must equal or exceed the heat necessaryto heat and fuse the ore introduced plus the sensible heat in theexhaust gas, plus radiation and cooling water losses from the cycloneburner. Having been given these requirements, the degree of preheatnecessary for the air supply to each cyclone burner, or the degree ofoxygen enrichment or both may readily be calculated by one skilled inmetallurgical and combustion calculations.

In most locations the primary fuel to be used in cyclone burner 2 willbe crushed coal, although this is not necessary. The process willoperate also upon coke, charcoal, petroleum or gas as the primary fuel.Lignite, brown coal and peat properly dried are workable fuels. Cycloneburner 1 has been described as fired only by gas from cyclone burner 2.However, this is not essential, albeit it is usually economicallydesirable. Under some circumstances such as where the metal beingproduced is readily reducible in the presence of large amounts of carbondioxide and/ or water vapor or where there is a The heat large demandfor heat as for steam raising or electric power, it may be moreeconomical to fire cyclone burner 1 with fuel other than the hot gasfrom cyclone burner 2. The omniverous characteristics of cyclone burnerswill permit almost any fuel to be employed here, either per se, or as anadjuvant to the hot gas from cyclone burner 2.

In the event the ore being treated is very lean resort may be had to theaddition with the pulverized ore of a metal or metal ore which willfollow through the process and which will be referred to as a washmetal. This metal serves the purpose of dissolving the desired metalsfrom the ore as they are reduced and removing them efiectually from thescene of the reaction. This wash metal may be introduced either as ametallic compound or ore in the metallic form. it may be either a puremetal or an alloy of metals. Under some circumstances it m y be possibleto select a wash metal which will be a solvent for the desired metal atthe reduction temperature and which will precipitate or partiallyprecipitate the desired metal upon cooling. An example of such a systemwould be the use of lead as a wash metal for copper bearing ores. inthis case the lead and copper are mutually soluble at high temperaturesand almost insoluble at low temperatures. As an example of a wash metalin which the metal desired is soluble in all proportions may bementioned copper for the recovery of nickel from the niclzeliferous oresmined in the vicinity of Sudbury, Ontario. These ores contain aboutthree percent nickel and copper combined as well as smaller values insilver, platinum and other metals. In this case a certain amount ofcopper may be kept circulating through the reduction apparatus acting asa wash metal to secure a more quantitative recovery of nickel, platinum,silver, etc. as a solute in molten copper. It is to be understood thatthe use of a wash metal is not always necessary and will depend upon theeconomic conditions prevailing at any given installation and upon suchfactors as the density of the metal sought, the liquidity of the slagproduced and the availability and cost of slagging materials which wouldserve to reduce the slag viscosity and assist in the operation of themetal and the ore.

Depending upon the nature of the metals sought to be recovered a washmetal may be selected which is either more diificult or less difiicultto reduce than the desired metal. Where the metal desired to be reducedis comparatively easy to reduce and of a high value resort may be had toa wash metal more difiicult to reduce but of less value. In such casethe wash metal should be intro duced as metal and into the reducingcyclone and excluded from contact with the oxidizing ambient in thecyclone 1. This metal may be added to reducing cyclone 2 either as asolid, or if the conservation of heat is imperative, in the molten form.An example of such a practice would be the use of cast iron borings as awash metal in treating copper ores or ores of other metals reducible byiron. Here the molten cast iron serves the dual function as a wash metaland a reducing agent, both functions tending to minimize the loss ofcopper values in the efiluent slag. As a matter of economy where easilyreducible metals such as copper are used as a wash metal they may alsobe introduced in cyclone burner 1 along with the ore to be treated.

Ferrosilicon may also be produced by adding to the second cyclone burnerfused silica and iron ore or alternatively fused iron silicates. Theproduction of ferrosilicon requires that the second cyclone be operatedvery hot and strongly reducing. The hotter the second cyclone isoperated and the more strongly reducing conditions are obtained, thehigher will be the percentage of silicon in the ferrosilicon.

As an alternative to the use of a wash metal or in conjunction therewithresort may be had to the use of centrifugal force to expedite theseparation of minute globules of metal from the molten flux. The useofcentrifugal force is particularly indicated where the difference inspecific gravity between the metal produced and the slag is insuflicientto give a clean separation.

I claim as my invention:

1. In a process for the combustion of fuel and the production of moltenmetal and a combustible gas, the steps of melting metal ore,transferring this molten ore to a cyclone burner operated underconditions reducing to said metal, adding to said cyclone burner asource of Wash metal, said wash metal being a solvent for the metalbeing reduced, tapping said metals and slag from the cyclone burner,said cyclone being operated at a temperature sufficient to liquefy orgasify all of the products of reaction except carbon, the sensible heatadded to the cyclone in the combustion air and fuel, plus the heat addedin the molten ore plus the heat of the combustion within the burnerbeing at least equal to the energy of reduction of the metal plus thesensible and latent heat of the gaseous products of combustion plus theheat of the molten metals and slag plus the heat abstracted by radiationand cooling Water.

2. In a process for the combustion of fuel and the production of moltenmetal and a combustible gas, the steps of melting metal ore,transferring this molten ore to a cyclone burner operated underconditions reducing to said metal, adding to said cyclone burner asource of Wash metal, said wash metal being a solvent for the metalbeing reduced at reduction temperatures but not at a lower temperature,tapping said metals and slag from the cyclone burner, said cyclone beingoperated at a temperature sufficient to liquefy or gasify all of theproducts of reaction except carbon, the sensible heat added to thecyclone in the combustion air and fuel, plus the heat added in themolten ore plus the heat of the combustion within the burner being atleast equal to the energy of reduction of the metal plus the sensibleand latent heat of the gaseous products of combustion plus the heat ofthe molten metals and slag plus the heat abstracted by radiation andcooling water.

3. In a process for the combustion of fuel and the production of moltennickel from nickel ore or concentrates, the steps of melting the ore,transferring this molten ore to a cyclone burner operating underconditions reducing to nickel, tapping said molten nickel and slag fromthe cyclone burner, said burner being operated at a temperaturesuficiently high to liquefy or gasify all of the reaction productsexcept carbon, the sensible heat added to the cyclone burner in thecombustion air and fuel plus the heat added in the molten ore plus theheat of combustion Within the burner being at least algebraically equalto the energy of the reduction of the nickel plus the sensible andlatent heat of the gaseous products of combustion plus the heat of themolten nickel and slag plus the heat abstracted by radiation and coolingWater.

4. In a process for the combustion of fuel and the production of moltennickel and a combustible gas, the steps of melting nickel ore,transferring this molten ore to a cyclone burner operated underconditions reducing to nickel, adding to said cyclone burner a source ofcopper other than that present in the nickel ore, tapping said nickeland copper and slag from the cyclone burner, said cyclone burner beingoperated at a temperature sufficient to liquefy or gasify all of theproducts of the reaction except carbon, the sensible heat added to thecyclone in the combustion air and fuel plus the heat added in the moltenore plus the heat of the combustion Within the burner being at leastequal to the energy of the reduction of the nickel and copper, plus thesensible and latent heat of the gaseous products of combustion, plus theheat of the molten nickel, copper and slag, plus the heat abstracted byradiation and cooling Water.

5. In a process for the production of molten nickel the steps of meltingthe nickeliferous ore in a cyclone 8, burner, transferring this moltenore to a second cyclone burner operated under conditions reducing thenickeliferous ore to nickel and tapping the molten nickel and slag fromthe second cyclone burner, said first cyclone burner employing as fuelgaseous effluent from the second cyclone burner, the heat introducedinto the second cyclone burner in the melted ore, in the air used forthe combustion of fuel, in the fuel and by tne combustion or" fueltherein equaling or exceeding the heat abstracted from said secondcyclone burner by the reduction of nickel plus the heat removed by thegaseous effluent plus the heat removed by the molten metal and slag plusthe heat removed by radiation and cooling water, and the heat introducedinto the first cyclone burner in the hot gaseous eflluent from thesecond cyclone burner plus the heat of combustion in this burner plusthe heat of the oxidizing gas used in the combustion equaling orexceeding the heat necessary to heat and melt the ore plus the heatabstracted by radiation and cooling plus the heat removed in the gaseouseflluent.

6. In a process for the production of molten nonferrous metal the stepsof melting nonferrous ore in a cyclone burner transferring this moltenore to a second cyclone burner operated under conditions reducing to thenonferrous metal and tapping the molten nonferrous metal and slag fromthe second cyclone burner, said first cyclone burner being fired atleast in part by the gaseous effluent from the second cyclone burner,the heat introduced into the second cyclone burner in the melted ore, inthe air used for the combustion of fuel, in the fuel and combustion offuel therein equaling or exceeding the heat abstracted from said secondcyclone burner by the reduction of the nonferrous metal plus the heatremoved by the gaseous efiluent plus the heat removed in the moltenmetal and slag plus the heat re moved by radiation and cooling water,and the heat introduced into the first cyclone burner in the hot gaseousefiluent from the second cyclone burner plus the heat of combustion indis burner plus the heat of the oxidizing gas used in'the combustionequaling or exceeding the heat necessary to heat and melt the nonferrousore plus the heat abstracted by radiation and cooling plus the heatremoved in the gaseous effluent.

7. In a process for the production of molten nickel the steps of meltingtogether in a cyclone burner nickeliferous ore and a source of coppertransferring the molten mixture to a second cyclone burner operatedunder conditions reducing the nickeliferous ore to nickel and tappingthe molten nickel copper alloy and slag from the second cyclone burner,said first cyclone burner being fired at least in part by the hotgaseous efiluent from the second cyclone burner, the heat introducedinto the second cyclone burner in the melted mixture, in the air used bythe combustion of fuel, and in the fuel and by the combustion of fueltherein equaling or exceeding the heat abstracted from said secondcyclone burner by the reduction of the material, plus the heat removedby the gaseous efiluent plus the heat removed in the molten metal andslag plus the heat removed by radiation and cooling Water, and the heatintroduced into the first cyclone burner in the hot gaseous eflluentfrom the second cyclone burner plus the heat of combustion in thisburner plus the heat of the oxidizing gas used in the combustionequaling or exceeding the heat necessary to heat and melt the ore plusthe heat abstracted by radiation and cooling plus the heat removed inthe gaseous efiluenti 8. In a process for the production of a moltenalloy of iron and nonferrous metal the steps of melting together in acyclone burner a mixture of iron ore and an ore of the nonferrous metal,transferring this molten material to a second cyclone burner operatedunder conditions capable of reducing to metal the most difiicultlyreducible ore, tapping the molten alloy and slag from the second cycloneburner, said first cyclone burner employing as fuel gaseous efiluentfrom said second cyclone burner, the

heat introduced into the second cyclone burner in the melted ores, inthe air used for the combustion of fuel, in the fuel and by thecombustion of fuel therein equaling or exceeding the heat abstractedfrom said second cyclone burner by the reduction of the metals plus theheat removed by the gaseous effluent, plus the heat removed in moltenmetal and slag plus the heat removed by radiation and cooling water, andthe heat introduced into the first cyclone burner in the hot gaseouseifiuent from the second cyclone burner plus the heat of combustion inthis burner plus the heat of the oxidizing gas used in the cornbustionequaling or exceeding the heat necessary to heat and melt the ores plusthe heat abstracted by radiation and cooling plus the heat removed inthe gaseous efiiuent.

9. in a process for the production of a molten alloy of iron andsilicon, the steps of melting iron ore and silica, adding these moltenmaterials to a cyclone burner operated under conditions capable ofreducing to metal at least a portion of the silica, tapping the moltenalloy and slag from the second cyclone burner, the heat introduced intothe cyclone burner in the melted ore, in the air used for the combustionof fuel, in the fuel and by the combustion of fuel therein equaling orexceeding the heat abstracted from the cyclone burner by the reductionof the metals plus the heat removed by the gaseous effluent, plus theheat removed in the molten metal and slag plus the heat removed byradiation and cooling water.

l0. in a process for the production of a molten alloy of iron and anonferrous metal the steps of melting an ore of iron and the nonferrousmetal, introducing this molten material into a cyclone burner operatedunder conditions capable of reducing to metal the most difiicultlyreducible ore and tapping the molten alloy from the cyclone burner, theheat introduced in the cyclone burner in the melted ores, in the airused for the combustion of fuel, in the fuel, and by the combustion offuel therein equaling or exceeding the heat abstracted from said cycloneburner by the reduction of the metals plus the heat removed by copper,introducing this molten material into a cyclone burner operated underconditions capable of reducing iron to metal and tapping the molten ironcopper alloy from the cyclone burner, the heat introduced in cycloneburner in the melted ore, in the air used for the combustion of fuel, inthe fuel, and by the combustion of fuel therein equalling or exceedingthe heat abstracted from such cyclone burner by the reduction or" themetals plus the heat removed by the gaseous effiuent plus theheatremoved in the molten metals and slag plus the heat removed by radiationand cooling water.

l2. In a process for the production of a molten alloy of iron andcopper, the steps of melting together metallic iron and copper ore,introducing this molten metal into a cyclone burner operated underconditions capable of re ducing oxides of iron to metal and tapping themolten iron copper alloy from the cyclone burner, the heat introducedinto the cyclone burner in the melted ore and iron, in the air used forthe combustion of fuel, in the fuel, and by the combustion of fueltherein equalling or eX- ceeding the heat abstracted from such cycloneburner by the reduction of the metals plus the heat removed by thegaseous eifiuent plus the heat removed in the molten metals and slagplus the heat removed by radiation and cooling water.

References Cited in the file of this patent UNITED STATES PATENTS861,593 De Laval July 30, 1903 1,815,888 Baily July 28, 1931 2,530,078Ramsing Nov. 14, 1950 2,581,597 Nissim Ian. 8, 1952

1. IN A PROCESS FOR THE COMBUSTION OF FUEL AND THE PRODUCTION OF MOLTENMETAL AND A COMBUSTIBLE GAS, THE STEPS OF MELTING METAL ORE,TRANSFERRING THIS MOLTEN ORE TO A CYCLONE BURNER OPERATED UNDERCONDITIONS REDUCING TO SAID METAL, ADDING TO SAID CYCLONE BURNER ASOURCE OF WASH METAL, SAID WASH BEING A SOLVENT FOR THE METAL BEINGREDUCED, TAPPING SAID METALS AND SLAG FROM THE CYCLONE BURNER, SAIDCYCLONE BEING OPERATED AT A TEMPERATURE SUFFICIENT TO LIQUEFY OR GASIFYALL OF THE PRODUCTS OF REACTION EXCEPT CARBON, THE SENSIBLE HEAT ADDEDTO THE CYCLONE IN THE COMBUSTION AIR AND FUEL, PLUS THE HEAT ADDED INTHE MOLTEN ORE PLUS THE HEAT OF THE COMBUSTION WITHIN THE BURNER BEINGAT LEAST EQUAL TO THE ENERGY OF REDUCTION OF THE METAL PLUS THE SENSIBLEAND LATENT HEAT OF THE GASEOUS PRODUCTS TO COMBUSTION PLUS THE HEAT OFTHE MOLTEN METALS AND SLAG PLUS THE HEAT ABSTRACTED BY RADIATION ANDCOOLING WATER.